1. Field of the Invention
The present invention relates to a transformer having a magnetic core and a conductive member, and a switching power supply unit provided with such transformer.
2. Description of the Related Art
Hitherto, various types of DC-DC converters have been proposed as a switching power supply unit and provided for practical use. Many of them are of a type in which a direct current input voltage is switched by switching operation of a switching circuit (inverter circuit) connected to a primary winding of a power converting transformer (transformer element), and the switched output (inverter output) is supplied to a secondary winding of the power converting transformer (transformer). A voltage appearing in the secondary winding in accordance with such switching operation of the switching circuit is rectified by a rectifier circuit, then the rectified voltage is converted into a direct current by a smoothing circuit and outputted.
This sort of switching power supply unit employs as a magnetic core of the above-mentioned transformer an E-shaped core (FE core, EI core, etc.) or a U-shaped core (UU core, UI core, etc.: see Japanese Patent Application Publication No. 2008-253113, for example), for example. In the case of the E-shaped core, winding is wound around a center leg so that a conductor passes between the outer legs and the center leg. On the other hand, in the U-shaped core, winding is wound around so that a conductor passes through the inner sides of the both legs thereof. Accordingly, the interval between the both legs of the U-shaped core is nearly twice as large as that between the center leg and the outer legs of the E-shaped core.